The present invention relates to a fuel injection control apparatus and a fuel injection control method for an internal combustion engine that directly inject fuel into a combustion chamber.
Japanese Unexamined Patent Publication No. 4-187841 discloses a direct injection internal combustion engine. In the prior art engine, fuel is directly injected into a combustion chamber. Then, a spark plug ignites a mixture of air and fuel formed in the combustion chamber. When the engine is cold, or when the engine is not warm, and the temperature inside the combustion chamber is low, the injected fuel resists vaporization. Thus, the amount of fuel that adheres to the inner wall of the combustion chamber increases. Therefore, the concentration of the air-fuel mixture about the spark plug is insufficient and the ignition and combustion are adversely affected. In the prior art engine, the amount of fuel injected during the compression stroke is increased when the engine is cold.
As described above, the amount of fuel that adheres to the inner wall of the combustion chamber increases when the engine is cold. This deteriorates the emission gas quality of the engine, that is, the amount of discharged unburned gas increases. To prevent the deterioration, fuel must be injected when the piston is relatively close to top dead center during the compression stroke. However, this causes unstable idling of the engine when the engine temperature increases.
The objective of the present invention is to provide a fuel injection control apparatus and a fuel injection control method for direct injection engine that suppress the deterioration of emission gas quality when the engine is cold and permit stable idling.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a fuel injection control apparatus for an engine is provided. An injector of the engine directly injects fuel into a combustion chamber. The apparatus includes a controller for controlling the injector. When the engine is cold, the controller controls the injector in a first mode, in which the fuel is injected during the compression stroke of the engine. The controller controls the injector to advance the timing of the injection of the first mode in accordance with an increase of the engine temperature.
The present invention also provides a fuel injection control method for an engine. Fuel is directly injected into a combustion chamber of the engine. The method includes injecting fuel during the compression stroke of the engine when the engine is cold and advancing the fuel injection timing in accordance with an increase of the engine temperature when the injection is executed during the compression stroke.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.